The present invention relates to an adhesive repellent coating and more particularly to a process for rendering surfaces adhesive repellent.
Adhesive repellent coatings obtained from compositions consisting of (1) a diorganopolysiloxane having terminal Si-bonded vinyl groups, but is otherwise free of aliphatic unsaturation, (2) a diorganopolysiloxane having at least 3 Si-bonded hydrogen atoms per molecule, (3) a vinylsiloxane platinum complex and (4) a compound which retards the addition of Si-bonded hydrogen to aliphatic multiple bond at room temperature have been described in German patent application DT-OS-No. 2,210,380.
Compared to the compositions described in German patent application No. DT-OS No. 2,210,380, the four (4) component compositions of the present invention are more stable, i.e., they have a longer "pot life", but they crosslink very rapidly at the crosslinking temperatures generally employed. Moreover, even 24 hours after their preparation, these compositions provide coatings which exhibit substantially the same adhesive repellency as freshly prepared compositions.
Also, German patent application No. DT-OS No. 2,427,738 describes coatings which are obtained from mixtures substantially free of solvents containing (1) a diorganopolysiloxane having terminal Si-bonded vinyl groups, but is otherwise free of aliphatic unsaturation, (2) an organopolysiloxane having at least 3 Si-bonded hydrogen atoms per molecule, (3) a platinum complex and (4) an organic compound which delays the addition of Si-bonded hydrogen to aliphatic multiple bonds at room temperature, in which the organic compound has a boiling point of at least 25.degree. C. at 760 mm Hg (absolute) and at least one aliphatic triple bond, such as 2-methyl-2-hydroxybutin-1-ol.
In contrast to the coatings described in German patent application No. DT-OS No. 2,427,738, the coatings of the present invention exhibit improved mechanical strength without having to employ organosiloxanes which contain an Si-bonded hydrogen in each of the terminal units and a methylvinylpolysiloxane having at least 3 Si-bonded vinyl groups per molecule [components (b) and (c) respectively of German patent application No. DT-OS No. 2,427,738]. Thus, the present invention provides coatings having improved mechanical strength without having to add organosiloxanes having terminal Si-bonded hydrogen atoms or methylvinylpolysiloxanes having at least 3 Si-bonded vinyl groups per molecule.
Therefore, it is an object of this invention to provide adhesive repellent coatings which exhibit improved mechanical strength. Another object of this invention is to provide compositions which can be crosslinked to form adhesive repellent coatings. Still another object of this invention is to form compositions which have a longer "pot life", but crosslink rapidly to form adhesive repellent coatings. A further object of this invention is to provide a process for preparing adhesive repellent coatings.